Lightly grease the edges and bottom of your slow cooker with olive oil (and/or you can line your slow cooker with foil).
Toss in garlic cloves, and drizzle with more olive oil. The cloves don't need to be in a single layer, but probably not higher than a few inches, or you may have uneven cooking. (Ask me how I know. Oops.)
Cook on low for 6+ hours, until cloves reach your desired consistency. You can stir a few times toward the end to get them evenly browned, as well.